Our invention relates to schottky barrier semiconductor devices and to a method of fabricating the same. The schottky semiconductor devices of our invention find typical use as diodes well adapted for high speed, high voltage applications.
A variety of high voltage blocking techniques have been suggested and used for schottky barrier or p-n junction semiconductor devices. Typical of such known techniques are the field plate and the field limiting ring. We object to the field plate because of its limited voltage blocking capability. The field limiting ring is also unsatisfactory by reason of difficulties involved in manufacturing the desired semiconductor devices of equally high voltage withstanding capabilities.
Another known approach is what we call the resistive schottky barrier field plate (RESP). The RESP techniques are disclosed in Ohtsuka et al. U.S. Pat. Appln. Ser. No. 277,333 filed Nov. 29, 1988, and Ohtsuka et al. U.S. Pat. Appln. Ser. No. 427,734 filed Oct. 26, 1989, both assigned to the assignee of the instant application, and are respectively U.S. Pat. No. 5,027,166 and an as yet unassigned number.
Typically, the RESP takes the form of a thin layer or ring of titanium oxide formed in direct contact with a semiconductor substrate so as to surround a barrier electrode thereon. An application of a reverse voltage to this semiconductor device results in the flow of reverse current through the RESP. Accordingly, the potential of the RESP becomes higher as it extends away from the barrier electrode, thereby lessening the field concentration at the periphery of the barrier electrode. The above cross referenced U.S. patent applications also teach the provision of another field plate over the RESP via an insulating layer.
We have found a weakness in the prior art RESP structures even though they are per se very well capable of accomplishing the objectives for which they have been designed. The voltage blocking capabilities of the prior art schottky semiconductor devices with the RESP structures have proved not so high as can be desired at the time of instantaneous transition from forward to reverse bias. The schottky semiconductor device is forward biased when the barrier electrode is positive, and the semiconductor substrate negative, and is reverse biased when the barrier electrode is negative, and the semiconductor substrate positive.